This invention relates generally to a method for manufacturing automotive seat assemblies, and more particularly to the use of fabrics with pre-bonded adhesives in the manufacture of automotive seat assemblies.
Styling and manufacturing considerations make it desirable to attach trim cover assemblies to cushion pads during the manufacture of automotive seat assemblies. The trim cover assemblies are typically comprised of cloth, leather, vinyl or other textile fabrics, and the cushion pads are typically comprised of polyurethane foam or rubberized hair. Several methods of attaching these components are currently being used.
Solvent-based or chemical adhesives, such as polyurethanes, may be used to attach trim cover assemblies to cushion pads. Use of these adhesives typically results in air emissions of hazardous chemicals, involves complicated material and waste handling procedures, and must be carefully engineered and monitored to reduce the possibility of exposing workers to hazardous materials.
Thermoplastic adhesives offer an environmentally friendly alternative to solvent-based or chemical adhesives. In conventional methods that use thermoplastic adhesives to attach the fabric material to the cushion material, a sheet of adhesive is placed between the components. The temperature of the adhesive is then raised to its softening point, typically through the application of heated vapor, such as steam. The thermoplastic adhesive forms a physical bond with the fabric material and the cushion material by simultaneously intruding into the fabric material and the cushion material.
Using these methods, it is typically more difficult to effectuate a suitable bond at the fabric material interface than it is to effectuate a suitable bond at the cushion material interface. This is particularly true for fabrics which have a conventional backcoat layer applied to the back of the fabric. The conventional backcoat layer consists of a latex or acrylic substance with a rubbery texture which is typically applied to fabric to prevent shrinkage and curling after it has been cut.
In addition, the heat required to effectuate a suitable bond at the fabric material interface is applied through a three-dimensional tool in conventional bonding methods. Because it is almost impossible to maintain a constant temperature across the entire surface of the tool during the bonding process, the tool must be heated beyond the ideal temperature to assure that the coolest section of the tool is at a high enough temperature to obtain a proper bond.
To overcome these problems, conventional attachment methods use large quantities of adhesive and long bonding cycle times to assure that a sufficient quantity of adhesive has migrated into the fabric material to obtain a suitable bond.
Because both the fabric material and the cushion material are heat sensitive, long bonding cycle times result in degradation of the fabric material and the cushion material, such as nap crush and loss of foam loft.
In addition, the improper application of the adhesive layer in conventional methods often results in quality problems in the finished seat. If the layer is improperly positioned or unintentionally omitted, the fabric material will not be properly attached to the cushion material. If wrinkles are introduced in the adhesive layer, they may be visible through the fabric.
In U.S. Pat. No. 4,692,199, a method for bonding an automotive trim cover assembly to a cushion pad is disclosed in which an impervious adhesive film is drawn by a vacuum against an automotive trim cover assembly; this film is placed in contact with the cushion pad and steam is used to diffuse the adhesive film into the fabric material and the cushion material. This method suffers from all of the process limitations and potential for quality defects noted above.
In U.S. Pat. No. 4,737,226, a method for manufacturing an automotive seat is disclosed in which a thermally weldable adhesive cloth is interposed between an automotive trim cover assembly and a cushion pad and then welded by means of heat and pressure to effectuate the bond between the fabric material and the cushion material. This method also exhibits all of the process limitations and potential for quality defects noted above.
In U.S. Pat. No. 4,795,517, an apparatus and process for shaping and covering cushion foam is disclosed in which a hot melt adhesive is placed between an automotive trim cover assembly and a cushion pad and superheated vapor is ejected through the fabric material and adhesive layer into the cushion material. This process also exhibits all of the process limitations and potential for quality defects noted above.
It is therefore desirable to provide an improved method for manufacturing automotive seat assemblies which allows for shorter bonding cycle times to effectuate a suitable bond between the fabric material and the cushion material and which alleviates the potential for quality defects noted above.